High temperature in summer can inhibit the growth of wasabi (Eutrema japonicum (Miq.) Kiudz.) and degrade the quality of its rhizome. Several materials for shading sunlight have been conventionally used for avoiding this negative effect during summer season, but adequate shading materials have not been selected based on scientific data. In the present study, we investigated effects of near-infrared ray cutting materials on growth of wasabi. Six types of the prototype nets, which effectively absorbed near-infrared ray in shortwave radiation, were used for the cultivation experiment. They had different shading ratios of 27–58% on the photosynthetically active radiation basis. Commercially available white-colored net with 39% shading ratio, which can reflect near-infrared ray effectively, and conventionally used black-colored net with 79% shading ratio were also applied. Five months later, the rhizome weight of wasabi was the highest under the prototype net with 38–46% shading ratio. The content of allyl isothiocyanate in wasabi rhizome was the highest under the prototype net with 38% shading ratio. These values were comparable to those under white-colored net and significantly higher than those under black-colored net. Surface temperature of black-painted brass boards placed horizontally was 1–2°C lower under the prototype net with 38% shading ratio than under white-colored net with 39% shading ratio during daytime. This may be attributed to the fact that downward shortwave radiation was significantly smaller under the prototype net than white-colored net, suggesting that the prototype net can cut near-infrared ray more efficiently. Our results suggest that the prototype nets with 38% shading ratio reduce negative temperature effect during summer season and promote growth of wasabi.

A network system of new coronavirus infection disease (COVID-19) is characterized using Biochemical systems theory (BST). A differential equation model is constructed in the framework of BST and the parameter values in the equations are determined from the infection data reported for the infected, recovered, and dead individuals (from January 15 to April 29, 2020) in Japan. Nondimensional analysis suggests that the time courses of dependent variables related to the infection are governed by two dimensionless parameters: G (the ratio of rate constants) and x₂₀ (the initial value for the ratio of infected individual number and population), and G must be greater than unity in order to certainly decrease the infected individual number to zero. The infection data in the initial stage indicates that if there was no action to protect, the infected individual number exponentially increased because G=0.0839143 < 1; for 120 million of the population in Japan, almost all persons were infected and the dead individual number increased to 16.8 million. Actually, however, the numbers of infected and dead individuals were only 16,305 and 749, respectively, suggesting that the contact rate was significantly reduced in a very short period of time. The analysis also indicates that x₂ takes a maximum when x₁ (the ratio of uninfected individual number and population) is equal to G. When the nosocomially infected individual number is equal to 10 % of the total number of infected individuals, the infected individual number never becomes zero unless the nosocomial infection is regulated even when the community infection is kept zero; in this case, the nosocomial infection must be aggressively reduced.

Treatment of air containing ethylene using the photocatalyst (UV-irradiated TiO₂) immobilized apart from activated carbon (AC) particles in a glass beaker was investigated both experimentally and theoretically. When only the AC particles were placed, the ethylene concentration initially dropped and became constant shortly because of reaching an equilibrium state. The degree of the initial drop increased and the equilibrium concentration decreased with an increase in the quantity of AC particles. When the photocatalyst and AC particles were simultaneously used, the ethylene concentration initially dropped owing to adsorption, but gradually decreasing and finally becoming zero owing to photocatalytic decomposition. When the quantity of AC particles was increased, the ethylene concentration dropped significantly, but reached zero by spending a long time. Theoretical analysis of this time-transient behavior using a mathematical model indicated that the photocatalyst cannot act on ethylene adsorbed in large amounts on AC particles unless the ethylene concentration in the air is lowered by the photocatalytic reaction and then ethylene on the AC particles is released.